1. Field of the Invention
The present invention relates to electrical connectors for connecting to a mother board a daughter board having a plurality of pads on a front edge thereof in a direction perpendicular, oblique, or parallel to the mother board.
2. Description of the Related Art
Recently, an increasing number of low-profile connectors are used for mounting memory modules. A conventional direct insertion type connector fails to meet the low-profile requirement and a variety of zero-insertion-force connectors are used as low-profile connectors.
Japanese patent application Kokai Nos. 230378/85 and 193473/88 disclose such zero-insertion-force connectors. Contact terminals for the electrical connectors are made by stamping a metal sheet having a predetermined thickness. These contact terminals have a very high spring constant because they are stamped from flat work. Consequently, if the spring constant is set to provide a satisfactory contact power for PC boards of the minimum thickness, an excessive force is applied to PC boards of the maximum thickness, causing breakage or difficulty to plug. In addition, the contact terminals are made by stamping so that a considerable amount of rare metal material is wasted. Moreover, the contact terminals made by stamping have contact sections cut by the stamping so that the contact sections must be plated after stamping, resulting in the increased manufacturing costs.
Japanese patent application Kokai No. 78168/90 discloses contact terminals made by stamping and bending a metal sheet instead of those made by stamping alone. By stamping and bending it is possible to avoid the above problems with those made by stamping alone.
FIGS. 12 and 13 show electrical connectors having such contact terminals. The electrical connectors are mounted on mother boards 10 to connect to the mother boards daughter boards 30 or PC boards on which memory modules are mounted. In FIG. 12(A), the daughter board 30 is going to be plugged into the electrical connector 20A which is mounted on the mother board 10. A plurality of terminal receiving grooves are provided in the front, bottom, and rear walls of an opening 25A in an insulation housing 21A of the electrical connector 20A for receiving contact terminals 40A.
The contact terminals are made by stamping and bending a resilient metal sheet so as to provide an upper contact portion 41A on the rear wall of the opening 25A and a lower contact portion 44A on the front wall. The connection sections 48A of every other contact terminals 40A extend downwardly from retaining sections 46A which are fixed to the receiving grooves on the rear wall. The connection sections 48A of the other contact terminals 40A extend downwardly from extension sections 47A which extend forwardly along the bottom wall. The connection sections 48A arranged in a zigzag fashion are inserted into through-holes on the mother board 10 for soldering.
A pair of latch levers 22A are provided on opposite sides of the opening 25A. Latch sections 23A are provided on the upper ends of the latch levers 22A. To plug the daughter board 30 in the electrical connector 20A on the mother board 10, the daughter board 20 is inserted obliquely into the opening 25A and rotated rearwardly as shown in FIG. 12(A). The daughter board 30 flexes the latch levers 22A outwardly and passes the latch sections 23A. The latch levers 22A snap to the original position to hold the daughter board 30 with the latch sections 23.
If the rotating force applied to the daughter board 30 is very large, the insulation housing 21A can be separated from the mother board 10 as shown in FIG. 12(B) because the insulation housing 21A is fixed only by the guide posts and connection sections of contact terminals.
In FIG. 13(A), the daughter board 30 is plugged in the electrical connector 20B mounted on the mother board 10. The electrical connector is substantially identical with that of FIG. 12 except for the shape of contact terminals 40B. The contact terminals 40B are also made by stamping and bending from a resilient metal sheet but the retaining sections are fixed in the terminal receiving grooves on the front wall of the opening 25B. The connection sections 48B of every other contact terminals 40B extend downwardly from the retaining sections 46B fixed in the receiving grooves on the front wall, while the connection sections 48B of the other contact terminals 40B extend downwardly from the extension sections 47B which extend rearwardly along the bottom wall. The connection sections 48B are arranged in a zigzag fashion and inserted into the through-holes of the mother board 10 for soldering.
In FIG. 13(A), the daughter board 30 is always biased forwardly. Consequently, the insulation housing 21B can be separated from the mother board 10 with passage of time as shown in FIG. 13(B).
To solve the above problems, the connection sections of contact terminals are reinforced, the insulation housing is reinforced or offset from the contact terminals, the guide posts are reinforced with flat holding fixings as disclosed in Japanese UM patent application Kokoku No. 22058/95, or the contact pressure is reduced. However, more material is used to reinforce the connection sections of contact terminals or the insulation housing, resulting in the increased manufacturing costs. If the insulation housing is offset from the contact terminals, it is not interchangeable with those of other companies. The use of special fixings increases the number of components, resulting in the increased manufacturing costs. The reduced contact pressure reduces the contact reliability.